Members of a massive galaxy-mapping project started a few years ago have just unveiled the first of several atlases they will produce of our Milky Way's galactic disc. These images of "cold dust" in the galaxy show where stars will ignite.

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Dubbed the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL), the project allows astronomers to observe submillimeter-wavelength light (between infra-red and radio waves), a "cool" area of the spectrum which reveals a lot of new information about our galactic core and the dust-clogged regions where stars come to life with a bang.

In this picture, astronomers say:

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The ATLASGAL submillimeter-wavelength data are shown in red, overlaid on a view of the region in infrared light . . . in green and blue. Some of the most prominent features visible in the image are (from left to right, top to bottom): - Messier 20 (the Trifid Nebula): A nebula containing an open cluster of stars as well as a stellar nursery. The name "Trifid" refers to the way that dense dust appears to divide it into three lobes at visible wavelengths. - Sagittarius B2 (Sgr B2): One of the largest clouds of molecular gas in the Milky Way, this dense region lies close to the Galactic Centre and is rich in many different interstellar molecules. - Galactic Centre: The centre of the Milky Way, home to a supermassive black hole more than four million times the mass of our Sun. It is about 25 000 light-years from Earth. - NGC 6357: A diffuse nebula containing the open cluster Pismis 24, home to several very massive stars. - NGC 6334: An emission nebula also known as the "Cat's Paw Nebula". - RCW 120: A region where an expanding bubble of ionised gas about ten light-years across is causing the surrounding material to collapse into dense clumps that are the birthplaces of new stars. - The Norma Arm: The region of somewhat brighter emission extending over about 10 degrees on the right-hand side of the image corresponds to the position of the Norma Arm, one of the spiral arms of the Milky Way.

The map is comprised of a very long, narrow slice of the galactic core which is two degrees wide and 40 degrees long. It's been very difficult for scientists to observe the galaxy in these cooler ranges because it requires extremely dry atmospheric conditions. Luckily, the APEX telescope array is located in a very arid region - the plateau of Chajnator in the Chilean Andes mountains.

According to a release about the new atlas:

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The interstellar medium - the material between the stars - is composed of gas and grains of cosmic dust, rather like fine sand or soot. However, the gas is mostly hydrogen and relatively difficult to detect, so astronomers often search for these dense regions by looking for the faint heat glow of the cosmic dust grains.

Submillimetre light allows astronomers to see these dust clouds shining, even though they obscure our view of the Universe at visible light wavelengths. Accordingly, the ATLASGAL map includes the denser central regions of our galaxy, in the direction of the constellation of Sagittarius - home to a supermassive black hole (ESO 46/08 - http://www.eso.org/public/outreach/press-rel/pr-2008/pr-46-08.html) - that are otherwise hidden behind a dark shroud of dust clouds.

The newly released map also reveals thousands of dense dust clumps, many never seen before, which mark the future birthplaces of massive stars. The clumps are typically a couple of light-years in size, and have masses of between ten and a few thousand times the mass of our Sun. In addition, ATLASGAL has captured images of beautiful filamentary structures and bubbles in the interstellar medium, blown by supernovae and the winds of bright stars.

Some striking highlights of the map include the centre of the Milky Way, the nearby massive and dense cloud of molecular gas called Sagittarius B2, and a bubble of expanding gas called RCW120, where the interstellar medium around the bubble is collapsing and forming new stars.